When forming a deep hole (a contact hole) having a high aspect ratio by plasma etching, an amount of radicals reaching a bottom of the hole decreases as the bottom of the hole becomes deeper, and an etching rate decreases.
When the etching rate decreases in a depth direction as the bottom of the hole becomes deeper, a bowing shape is formed in the hole that has a hole diameter larger in a lower position than in an upper position (see [b] in FIG. 2). Moreover, when a side wall of the hole is etched as well as the bottom of the hole during the etching, an aspect ratio thereof decreases because of an increased critical dimension value (Critical Dimension) that is a diameter of the top of the hole, and desired semiconductor device properties cannot be obtained.
In the meantime, there are a variety of methods for depositing a film, and for example, Patent Document 1 discloses a technique that protects a device by depositing a dense dielectric layer on the device by an ALD (Atomic Layer Deposition) method.